Differential Diagnosis for Elevated Anion Gap and Low CO2

Single Most Likely Diagnosis

• Diabetic Ketoacidosis (DKA): This condition is characterized by hyperglycemia, metabolic acidosis with an elevated anion gap, and the presence of ketones. The low CO2 level is consistent with a compensatory response to the metabolic acidosis, where the body tries to blow off CO2 to reduce acidity.

Other Likely Diagnoses

• Lactic Acidosis: This can occur due to tissue hypoxia, sepsis, or biguanide (metformin) overdose. It presents with an elevated anion gap metabolic acidosis and low CO2 as the body attempts to compensate for the acidosis.
• Renal Failure: Acute or chronic renal failure can lead to the accumulation of organic acids, resulting in an elevated anion gap metabolic acidosis. The low CO2 is part of the compensatory mechanism.

Do Not Miss Diagnoses

• Toxic Alcohol Ingestion (e.g., Methanol, Ethylene Glycol): These ingestions can lead to severe metabolic acidosis with an elevated anion gap and are medical emergencies. Early recognition and treatment are crucial to prevent serious complications, including death.
• Salicylate Overdose: Aspirin overdose can cause a mixed acid-base disorder, including an elevated anion gap metabolic acidosis and respiratory alkalosis, which would result in a low CO2 level.

Rare Diagnoses

• Ketone Body Production Disorders: Rare genetic disorders affecting the metabolism of fatty acids and ketone bodies can lead to episodes of metabolic acidosis with an elevated anion gap.
• Pyroglutamic Acidemia: A rare condition caused by an inborn error of metabolism leading to the accumulation of pyroglutamic acid, resulting in an elevated anion gap metabolic acidosis.

Each of these diagnoses has a distinct set of clinical and laboratory features that can help guide the diagnosis. It's crucial to consider the patient's clinical presentation, history, and other laboratory findings when evaluating these possibilities.